The present invention relates to a coffee percolator of the type including a fresh water container, a heatable hot water chamber receiving water from said fresh water container through a non-return valve, and a riser pipe extending from said hot water chamber to a boiling water outlet.
Coffee percolators of the type most commonly encountered in the market include an electrically heated hot water or boiling chamber having a capacity of only a few cubic centimeters of water. This small amount of water is heated to its boiling point within the boiling chamber and then discharged therefrom to flow over the ground coffee contained in a filter cup. The preparation of a desired amount of coffee of for instance six to eight cups with a percolator of this type requires about fifty boiling-discharging-filling cycles of the hot water chamber, resulting in the hot water being supplied substantially continuously to the ground coffee over a period of about ten to twelve minutes.
Reduction of the percolation time is not practicable with a percolator of this type, because the hot water chamber employed therein would become overheated if the power supplied thereto were to exceed bout 500 to 600 watts. Owing mainly to the long percolation time, but also as a result of several additional factors, the ground coffee is very strongly leached, resulting in the coffee beverage containing acrimonious substances and acids. One of the additional factors is that, over the entire percolation period, sufficiently hot heated water generally reaches only the central area of the ground coffee, while the border areas cool rather rapidly. Also, the heated water in this type of percolator reaches the ground coffee at a temperature of less than bout 85.degree. C. For all these reasons, many coffee connoisseurs prefer hand-brewed coffee and consider machine-brewed coffee stale and of insufficiently developed aroma.
It is therefore an object of the present invention to provide a coffee percolator with the aid of which it is possible to prepare a coffee beverage of improved flavor characteristics.
In contrast to the known coffee percolators referred to above, a percolator according to the invention has a hot water chamber of substantially increased volume, about 30 to 60% of the volume of the water needed for a full infusion. As a result, the heated water is supplied to the ground coffee in the form of only two or three relatively large-volume charges, so that the entire volume of the ground coffee is infused at a higher temperature than in the case of the above discussed known percolators. This enables the entire percolation process to be accomplished within a short overall percolation time of about 2.5 to 4 minutes, resulting in the coffee beverage containing a maximum of aromatic substances and only a small proportion of flavor-impairing and other extraction substances. A further advantage of this coffee percolator resides in the fact that it does not produce the disagreeable gurgling noises common to percolators having a small-volume hot water chamber, and that its tendency to become calcified is considerably reduced.
In a preferred embodiment, the hot water chamber is provided immediately below a fresh water container and a common wall between them defines a bottom wall for the fresh water container. In this bottom wall, there is slidably mounted a ventilation pipe which extends downwardly into the hot water chamber. This permits the amount of water entering the hot water chamber to be varied. This also permits the number of boiling-discharging-filling cycles performed by the percolator to be varied. In the case, for instance, of an eight-cup percolator, this feature permits a smaller volume of coffee of, for instance, six cups to be prepare without varying the number of the operating cycles. This feature additionally permits the overall percolation time to be varied, although only to a limited degree. The ventilation pipe also includes a check valve for preventing the expulsion of water from the hot water chamber into the fresh water container.
Before entering into a discussion of the preferred embodiments, it may be helpful to consider several specific aspects of the present percolator. As the amount of water discharged from the hot water chamber in one operating cycle is relatively great, it is preferred to take specific precautions against the infusion water entering the filter cup at an excessive speed. The relatively high power input to a coffee percolator of this type (in the case of an eight-cup percolator, for instance about 1100 watts) results in a high steam pressure, which causes the infusion water evaporating in the hot water chamber to contain a relatively great proportion of steam upon discharge. In the absence of any precautions, the danger exists that the infusion water will splash out of the filter cup or that the ground coffee will be pushed up excessively along the walls of the filter. The invention contemplates various features which may be employed by themselves or in any combination for countering these dangers.
In accordance with another aspect of the invention, steam pressure generated in the hot water chamber is counteracted by releasing steam prior to expulsion of the last bit of water remaining in the hot water chamber, and this steam mixes with the water flowing through the riser pipe. This is effective to prevent the remainder of the water from being expelled at an excessive speed. This steam release permits a relatively high heating input to be applied so as to accomplish the entire percolation process in a short time. Embodiments are disclosed in which steam release is achieved by providing an elongated slot or a series of spaced holes near the inlet end of the riser pipe, by cutting the inlet end of the riser pipe obliquely, and by providing branch pipes of different lengths at the inlet end of the riser pipe.
Although a steam outlet opening of increasing size already results in a considerable improvement, the best results are achieved with a steam outlet opening of continuously increasing size.